1. Field of the Invention
The present invention relates to a device for optically regenerating pulses. The invention also relates to an optical transmission installation including such a device, and to the use of the device for regenerating dispersion-managed (DM) soliton pulses.
More precisely, the invention relates to a device for optically regenerating pulses, the device being of the type comprising time synchronization means and means for stabilizing the intensity fluctuations of the pulses.
2. Description of Prior Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Devices are known for optically regenerating pulses that are effective in particular for regenerating pulses of the soliton type. Those devices implement optical regeneration of the reamplification, reshaping, and retiming (3R) type.
Soliton type pulses have the property of propagating without deformation in a non-linear medium since these particular pulses constitute a solution to the non-linear Schrödinger equation. Nevertheless, the accumulation of amplified spontaneous emission noise disturbs the propagation of such pulses by generating intensity fluctuations and time jitter (known as Gordon-Haus jitter), whence the need to regenerate them optically.
In addition, for a soliton pulse to propagate without deformation and to benefit from ideal optical regeneration, the emitted pulses must not be too close together, which imposes narrow time widths for soliton pulses, and thus a broad spectrum. This leads to problems with ultra-dense wavelength division multiplexing (WDM) type optical transmission applications, in particular at data rates exceeding 40 gibabits per second (Gbit/s) and over long distances of the transoceanic type.
An advantageous solution for that type of application is to use DM type soliton pulses which provide significant advantages over conventional soliton pulses for high capacity transmission systems. However, a DM soliton is much less suitable than a conventional soliton for 3R regeneration.
For a DM type soliton pulse, a known device providing optical regeneration is described in particular in the document entitled “Stability of synchronous intensity modulation control of 40 Gbit/s dispersion-managed soliton transmissions” by Erwan Pincemin, Olivier Audouin, Bruno Dany, and Stefan Wabnitz, published in the Journal of Lightwave Technology, Vol. 19, No. 5, May 2001. The solution recommended in that document consists in using a synchronous intensity modulator disposed at a suitable location along the optical fiber for transmitting DM soliton pulses. However, in order to be efficient, that device must also suppress noise, and in particular amplified spontaneous emission noise. To do that, the synchronous intensity modulator must have an extinction ratio that is sufficient, e.g. 10 decibels (dB), which makes it necessary to use short DM solitons that present a broad spectrum. The synchronous intensity modulator must not have a negative impact on the time width of the DM soliton pulse.
The invention seeks to remedy the above-mentioned drawbacks by providing a device for optically regenerating pulses, in particular DM soliton pulses, with said device being capable of optically regenerating such pulses while enabling them to be used for ultra-dense WDM type transmissions at a very high data rate.